Cell populations are presented with a vast array of small molecules that interact with surface membrane receptor structures and consequently influence the behavior of the tissue. The purpose of this project is to study spatial associations and interactions among different receptor populations that coexist in the same tissue. The objectives will be pursued through the study of several different types of receptors (i.e., catecholamine, cholinergic, insulin and nerve growth factor). The cell populations to be studied are skeletal muscle and sympathetic ganglia. The relationships between the different receptor populations will be studied both at the level of the intact cells in culture and in membrane fractions derived from the tissues. The membrane fractions will include subfractions obtained both from the standard differential and density gradient centrifugation approach and from a multiple stage membrane affinity isolation approach described in the methods. The goal is to describe and separate integrative relationships mediated by cellular metabolic processes from those mediated at the membrane level. In summation, it is expected that the experiments described in this program will increase the understanding of the mechanisms by which the array of small molecule inputs modulate the behavior of a given cell population.